Pretty sure this change was wrong. I.e. the title needs to be added back somewhere else. This currently only works because the hook_menu() menu item has a 'title' and if '#title' is not set and the title resolver doesn't return anything either, drupal_get_title() is called which checks the menu item title. I guess simply adding $form['#title'] would be the easiest.

Well hook_menu() is only for menu links now. That should not be relied on for the actual page output. The fact that it currently works is only an artefact of legacy code. I'm not going to judge whether that is ridiculous or not, but that's simply how things are at the moment. Unless I'm completely missing something, needless to say.